An SSL certificate is a server digital certificate that complies with the SSL (Secure Sockets Layer) protocol.  The SSL protocol was developed by Netscape Communications.

SSL serves as a solution for layered data security between application protocols (such as HTTP, Telnet, and FTP) and TCP/IP. It is based on public key cryptography, and enables data encryption, server authentication, data integrity, and optional client authentication for TCP/IP connections. Owing to its ability to solve security problems inherent in plain text transmission over the Internet, this protocol rapidly gained popularity and has become an international standard.

SSL certificates are issued by a trusted root certificate authority in the web browser after the server authentication is completed. An SSL certificate provides both website authentication and encrypted transmission.